In the fields of displays for use in television receivers and information terminals, studies have been made for replacing conventionally mainstream cathode ray tubes (CRT) with flat-panel displays which are to comply with demands for a decrease in thickness, a decrease in weight, a larger screen and a high fineness. Such flat panel displays include a liquid crystal display (LCD), an electroluminescence display (ELD), a plasma display panel (PDP) and a cold cathode field emission display (FED). Of these, a liquid crystal display is widely used as a display for an information terminal. For applying the liquid crystal display to a floor-type television receiver, however, it still has problems to be solved concerning a higher brightness and an increase in size. In contrast, a cold cathode field emission display uses cold cathode field emission devices (to be sometimes referred to as “field emission device” hereinafter) capable of emitting electrons from a solid into a vacuum on the basis of a quantum tunnel effect without relying on thermal excitation, and it is of great interest from the viewpoints of a high brightness and a low power consumption.
FIGS. 29 and 4 shows a cold cathode field emission display to which the field emission devices are applied (to be sometimes referred to as “display” hereinafter). FIG. 29 is a schematic partial end view of the conventional display, and FIG. 4 is a schematic partial perspective view of a cathode panel CP.
The field emission device shown in FIG. 29 is a so-called Spindt-type field emission device having a conical electron-emitting portion. Such a field emission device comprises a cathode electrode 11 formed on a supporting member 10, an insulating layer 12 formed on the supporting member 10 and the cathode electrode 11, a gate electrode 13 formed on the insulating layer 12, an opening portion 14 formed through the gate electrode 13 and the insulating layer 12 (a first opening portion 14A formed through the gate electrode 13 and a second opening portion 14B formed through the insulating layer 12), and a conical electron-emitting portion 15 formed on the cathode electrode 11 positioned in the bottom portion of the second opening portion 14B. Generally, the cathode electrode 11 and the gate electrode 13 are formed in the form of a stripe each in directions in which the projection images of these two electrodes cross each other at right angles. Generally, a plurality of field emission devices are arranged in a region (corresponding to one pixel, and the region will be called an “overlap region” or an “electron-emitting region” hereinafter) where the projection images of the above two electrodes overlap. Further, generally, such electron-emitting regions are arranged in the form of a two-dimensional matrix within an effective field (which works as an actual display portion) of the cathode panel CP.
An anode panel AP comprises a substrate 30, phosphor layers 31 (31R, 31B, 31G) being formed on the substrate 30 and having a predetermined pattern, and an anode electrode 220 formed thereon. The anode electrode 220 has the form of one sheet covering the effective field and is formed, for example, of an aluminum thin film. Generally provided between an anode-electrode control circuit 43 and the anode electrode 220 is a resister R0 (resistance value 10 MΩ in a shown example) for preventing excess current and discharge. The resister R0 is provided outside the substrate.
Each pixel is constituted of a group of the field emission devices formed on the overlap region of the cathode electrode 11 and the gate electrode 13 of the cathode panel side and the phosphor layer 31 of the anode panel side arranged so as to face the group of the field emission devices. In the effective field, such pixels are arranged on the order, for example, of hundreds of thousands to several millions. A black matrix 32 is formed on the substrate 30 between one phosphor layer 31 and another phosphor layer 31, and a separation wall 33 is formed on the black matrix 32.
The anode panel AP and the cathode panel CP are arranged such that the electron-emitting regions and the phosphor layers 31 are opposed to each other, and the anode panel AP and the cathode panel CP are bonded to each other in their circumferential portions through a frame 35, whereby the display is produced. In an ineffective field which surrounds the effective field and where a peripheral circuit for selecting pixels is provided, a through-hole (not shown) for vacuuming is provided, and a tip tube (not shown) is connected to the through-hole and sealed after vacuuming. That is, a space surrounded by the anode panel AP, the cathode panel CP and the frame 35 is in a vacuum state.
A relatively negative voltage is applied to the cathode electrode 11 from a cathode-electrode control circuit 41, a relatively positive voltage is applied to the gate electrode 13 from a gate-electrode control circuit 42, and a positive voltage having a higher level than the voltage applied to the gate electrode 13 is applied to the anode electrode 220 from an anode-electrode control circuit 43. When such a display is used for displaying on its screen, a scanning signal is inputted to the cathode electrode 11 from the cathode-electrode control circuit 41, and a video signal is inputted to the gate electrode 13 from the gate-electrode control circuit 42. Due to an electric field generated when a voltage is applied between the cathode electrode 11 and the gate electrode 13, electrons are emitted from the electron-emitting portion 15 on the basis of a quantum tunnel effect, and the electrons are attracted toward the anode electrode 220 and collide with the phosphor layer 31. As a result, the phosphor layer 31 is excited to emit light, and a desired image can be obtained. That is, the working of the display is controlled, in principle, by a voltage applied to the gate electrode 13 and a voltage applied to the electron-emitting portion 15 through the cathode electrode 11.
In JP-A-2001-243893, Applicant proposes a display panel in which an anode electrode is constituted of a plurality of anode electrode units.
Meanwhile, in the above display, the distance between the anode panel AP and the cathode panel CP is about 1 mm at the largest, and an abnormal discharge (vacuum arc discharge) is liable to take place between the field emission device on the cathode panel and the anode electrode 220 on the anode panel AP. When the abnormal discharge takes place, not only the display quality is impaired, but also the field emission device or the anode electrode 220 is damaged.
In a mechanism in which a discharge takes place in a vacuum space, first, electrons and ions that are emitted from the field emission device under a strong electric field work as a trigger to cause a small-scaled discharge. And, energy is supplied to the anode electrode 220 from the anode-electrode control circuit 43, the anode electrode 220 is locally temperature-increased, and an occluded gas inside the anode electrode 220 is released, or a material constituting the anode electrode 220 is caused to vaporize, so that the small-scaled discharge presumably grows to be an abnormal discharge. Besides the anode-electrode control circuit 43, energy accumulated in an electrostatic capacity formed between the anode electrode 220 and the field emission device may possibly work as a source for supplying energy that promotes the growth to the abnormal discharge.
For inhibiting the abnormal discharge (vacuum arc discharge), it is effective to control the emission of electrons and ions which trigger the discharge, while it is required to control the particles extremely strictly therefor. In a general production process of the anode panels AP or the display panels using the anode panels AP, practicing the above control involves great technical difficulties.
While the anode electrode unit proposed in JP-A-2001-243893 has an effect on inhibiting the growth of a small-scale discharge to a large-scale discharge, it has been found to still have room for further improvements.
It is therefore an object of the present invention to provide a cold cathode field emission display having an anode electrode that is so structured as to more reliably inhibit the growth of a small-scale discharge to a large-scale discharge.